1. Field of the Invention
The present invention relates to a surface shape measurement apparatus for measuring a shape of a surface of an object to be examined.
2. Description of Related Art
When light is irradiated onto a surface of an object to be examined, through a reference grid formed with a predetermined spacing, and the object surface is observed through the reference grid from a direction different from a direction of the light irradiation, moirxc3xa9 fringes are obtained (observed) due to the reference grid and a grid pattern projected on the object surface. A shape of the object surface can be measured based on the moirxc3xa9 fringes. As a method for measuring it, a phase shift method has been known, under which moirxc3xa9 fringes are shifted by causing a minute displacement of a distance between a reference grid and an object surface to be measured.
However, the above-described method involves the following problem. For example, measuring a shape of a surface of a semiconductor wafer being 300 mm in diameter require a reference grid which is commensurate in size with the wafer; it may be difficult to cause a minute movement of such a large-sized reference grid in parallel to the object surface with good accuracy. In addition, translating the reference grid to measure up to a required degree of measurement accuracy will entail a complicated mechanism.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a surface shape measuring apparatus with which a shape of a surface of a large-sized object to be examined can be measured by a simple mechanism.
To achieve the objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, a surface shape measurement apparatus for measuring a shape of a surface of an object to be examined is provided with: a stage on which the object is rested; a reference grid disposed in parallel to the stage; illumination means for illuminating the reference grid and projecting a grid pattern onto the surface of the object; photographing means for photographing the grid pattern projected onto the object surface through the reference grid and obtaining an image of moirxc3xa9 fringes; rotation means for rotating the reference grid about an axis normal to a grid surface of the reference grid; and analysis means for analyzing the shape of the object surface based on information about a rotation angle of the reference grid and intensity of the moirxc3xa9 fringes.
In another aspect of the invention, a surface shape measurement apparatus for measuring a shape of a surface of an object to be examined is provided with: a stage on which the object is rest; a grid plate having a reference grid and being disposed in parallel to the stage; an illumination unit placed opposite to the stage with respect to the grid plate such that light obliquely enters the object surface through the reference grid; a photographing unit placed opposite to the stage with respect to the grid plate such that the light from the object surface is received through the reference grid and that an image of moirxc3xa9 fringes is obtained; a rotation unit which rotates the grid plate so as to rotate the reference grid about an axis normal to a grid surface of the reference grid; and an analysis unit which analyzes the shape of the object surface based on information about a rotation angle of the reference grid and intensity of the moirxc3xa9 fringes.
Additional objects and advantages of the invention are set forth in the following description, are obvious from the description, or may be learned by practicing the invention. The objects and advantages of the invention may be realized and attained by means of instrumentalities and combinations particularly pointed out in the claims.